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Whether people prefer coffee or tea may boil down to a matter of taste genetics.

People with a version of a gene that increases sensitivity to the bitter flavor of caffeine tend to be coffee drinkers, researchers report online November 15 in Scientific Reports. Tea drinkers tended to be less sensitive to caffeine’s bitter taste, but have versions of genes that increase sensitivity to the bitterness of other chemicals, the researchers found.

It’s long been thought that people avoid eating bitter foods because bitterness is an indicator of poison, says John Hayes, a taste researcher at Penn State who was not involved in the study. The coffee and tea findings help challenge that “overly simplistic ‘bitter is always bad, let’s avoid it’” view, he says.

In the new study, researchers examined DNA variants of genes involved in detecting the bitter taste of the chemicals caffeine, quinine — that bitter taste in tonic water — and propylthiouracil, or PROP, a synthetic chemical not naturally found in food or drink. Other bitter components naturally in coffee and tea may trigger the same taste responses as quinine and PROP do, Hayes says.

Researchers in Australia, the United States and England examined DNA from more than 400,000 participants in the UK Biobank, a repository of genetic data for medical research. Participants also reported other information about their health and lifestyle, including how much tea or coffee they drink each day.

The team added up each person’s variants in the taste genes, creating a genetic score for how intensely the person tastes each of the bitter chemicals. The researchers then compared those scores to the people’s reported beverage choices.

People who had the highest genetic score for detecting caffeine’s bitterness were 20 percent more likely to be heavy coffee drinkers, downing four or more cups a day, than those without the increased sensitivity, the researchers calculate.

Coffee drinkers may have learned to enjoy caffeine’s bitterness because it’s a sign of the buzz the chemical provides. But tea drinkers may not actually like the bitterness of PROP and quinine, says Cornelis, a nutritional and genetic epidemiologist at Northwestern University Feinberg School of Medicine in Chicago. Rather, people tend to stick with either coffee or tea, so the tea result may just be a rejection of coffee.

It’s unclear how big of a role bitter taste genes play in determining whether someone chooses coffee or tea. In previous studies that sought genetic variants linked to coffee consumption, “taste genes did not come up,” Cornelis says. Instead, genes involved in breaking down caffeine may play bigger role in determining how much coffee or tea people drink (SN: 10/1/16, p. 14).